Create and instantiate a class

[gregghz]

object Macro {
  inline def create[T]: T = ${impl}
  private def impl[T: Type](using Quotes): Expr[T] = {
    val t = Type.of[T]

    '{
      final class SomeRandomName extends $t {
        def someMethod(): String = ""
      }
      new SomeRandomName()
    }    
  }
}

This fails with T is not a class type.

I'm hoping to write this macro such that this code:

val x = Macro.create[SomeClass]

expands into (or something equivalent):

val x = {
  final class SomeRandomName extends SomeClass {
    def someMethod(): String = ""
  }
  new SomeRandomName()
}

I've been struggling to know how to use the reflect API and build an AST from that mostly because the results of term.show are different than how you actually use the API (for example, when printing, TypeDef shows two parameters but the only constructors that exist take one or three parameters -- and for copy, it's unclear to me what the original tree is supposed to be and what happens when you "copy").

[bishabosha]

I suggest that you look at the examples in this PR:
#14124 but you will be using experimental API (released in Scala 3.1.3-RC2)

[gregghz]

do you happen to know how to use an @experimental method (like Symbol.newClass) inside an inline method?

https://scastie.scala-lang.org/CCUeignRSJOnYEBa8aJTWg

I filed a bug for this but I think it might be intentional? #15133

[nicolasstucki]

A simpler approach is to use a nightly build of the compiler. There you will not need to use the @experimental annotation in your code.

[nicolasstucki]

Using the current nightly will not work due to #15133. The nightly published after #15147 is merged will work.

[gregghz]

bummer, looks like the next RC got cut without this being merged :(